Work arms, e.g. of tire assembling-disassembling machines or plate/plane support arms, such as raising machine arms (e. g. cranes) designed to displace loads between different levels, are suitably handled by means of an actuator comprising, for example, a fluid-operated group having its cylinder anchored to a base (e. g. a base of a crane) and a piston rod protruding from the cylinder, whose free end is designed to support a work arm.
First of all, with such a solution a jack or another linear actuator for each working arm should be used. Moreover, when very high levels are to be reached, or loads are to be moved between two quite distant levels, a jack suitable for carrying out a stroke of considerable length must be used, which involves high costs. However, if the jack does not work in a vertical trim, a bending moment approximately proportional to the length of the jack occurs at the free end of the stem. Thus, a substantial resistant force arises, that must be overcome to obtain a stable and safe operation of the load handling device.
So far as the specific field of the tire assembling-disassembling machines is concerned, as it is known, such machines usually comprise a base, a wheel support table mounted for rotation on the base, one or more columns rising from the base, and one or more work arms cantileverwise extending from the or each column, each work arm being designed to support a respective tool at the free end thereof. Such tools are the so-called “bead releasing tools”, that are employed to bead release, i. e. to detach the beads of a tire mounted on a wheel rim from its respective wheel rim edge. One or more work arms, generally extendable-retractable arms, generally extend from the column or columns, and each supports a respective assembling-disassembling tool designed to assist in mounting/dismounting operations by forcing a tire bead engaged by the tool to follow a pre-determined path by causing the engaged edge of the tire to be deformed so as to force it to pass over the wheel rim edge facing it.
Each work arm is controlled by a respective linear actuator, usually a pneumatic jack.
During tire assembling-disassembling operations a plurality of tools, typically two tools, must be simultaneously operated sometimes, and this obviously results in the need of operating as many actuators as are bead releasing tools to be controlled.
To this end, some tire assembling-disassembling machines are provided with bead releasing tools designed to be simultaneously or separately operated on opposite sides of a tire, e. g. when bead releasing, assembling or disassembling operations are to be accomplished.